A group of teenage boys have told of an hour-long rescue in which they pulled three struggling swimmers from ferocious seas.

The current was so strong and waves so powerful at Waipatiki Beach in Hawkes Bay on Saturday that it took 45 minutes for the group of Napier teens to swim 250m to reach the three female swimmers - one so close to drowning she was losing consciousness.

A 21-year-old woman had been carried 250m offshore in a rip, and her two younger cousins, one aged 16 and the other about 12, had also got into trouble trying to help her, said Hawkes Bay Police Senior Sergeant Mike Stevenson.

"The waves were just huge, and there was a huge big swell," said Lucan Battison, 14. "You dived under the waves to go out and they just pushed you back in."

The boys began to swim out, with Lucan reaching the youngest girl first and 15-year-old Callum Williams continuing to where the oldest was struggling.

"Everyone was pointing the direction where to go and she was way, way out past the breakwater," said Callum. "So I just kept on going and it took ages to get out there and I was getting really tired."

Daniel Troy, 17, and his brother Kris, 15, helped Lucan bring the young girl into shore.

"She was in a bit of shock and everyone was covering her in towels to keep her warm," said Lucan. "Even walking back in everyone was just struggling to stand because the current was so strong."

As time went on, there was panic on the beach as the girls' family watched in horror and other beachgoers began to step in.

A kayaker, Andrew White, and an unidentified surfer managed to take a lifejacket to the second girl.

Nick Roydhouse, 17 and another boy, Izaiah Lange, 15, helped bring the 16-year-old to shore where she was cared for by onlookers.

When Callum reached the 21-year-old she was coughing up water and struggling to stay afloat, he said.

"I saw her face when I got carried up by a wave and she was going under the water and spewing up water.

"So I put her arm around my shoulder and kept saying 'Breathe, breathe, it's going to be okay, I'm here'."

The pair had to navigate under waves, and were dragged back by the woman's cotton clothes.

"The waves were absolutely smashing us ... I was just trying to talk to her and ask her questions to keep her conscious and just as I was getting into the breakwater this surfboarder came along."

The surfer was helped by the boys to lift the woman on to his board and carry her into shore.